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The gut microbiota influences host epigenetics by fermenting dietary fiber into butyrate. Although butyrate could promote histone acetylation by inhibiting histone deacetylases, it may also undergo oxidation to acetyl-CoA, a necessary cofactor for histone acetyltransferases. Here, we find that epithelial cells from germ-free mice harbor a loss of histone H4 acetylation across the genome except at promoter regions. Using stable isotope tracing in vivo with 13C-labeled fiber, we demonstrate that the microbiota supplies carbon for histone acetylation. Subsequent metabolomic profiling revealed hundreds of labeled molecules and supported a microbial contribution to host fatty acid metabolism, which declined in response to colitis and correlated with reduced expression of genes involved in fatty acid oxidation. These results illuminate the flow of carbon from the diet to the host via the microbiota, disruptions to which may affect energy homeostasis in the distal gut and contribute to the development of colitis.

International audience; The discovery of tumor-associated antigens recognized by T lymphocytes opens the possibility of vaccinating cancer patients with defined antigens. However, one of the major limitation of peptide-based vaccines is the low immunogenicity of antigenic peptides. Interestingly, if these epitopes are directly delivered into the cytoplasm of antigen presenting cells, they can be efficiently presented via the direct MHC class I presentation pathway. To improve antigen entry, one promising approach is the use of cell penetrating peptides (CPPs). However, most studies use a covalent binding of the CPP with the antigen. In the present study, we focused on the C-terminal domain of Vpr which was previously demonstrated to efficiently deliver plasmid DNA into cells. We provide evidence that the peptides Vpr55-91 and Vpr55-82 possess the capacity of delivering proteins and epitopes into cell lines as well as into human primary dendritic cells, without the necessicity for a chemical linkage. Moreover, immunization of HLA-A2 transgenic mice with Vpr55-91 as the sole adjuvant is able to induce antigen-specific cytotoxic T lymphocytes against multiple tumor epitopes.

We describe the Phase II HapMap, which characterizes over 3.1 million human single nucleotide polymorphisms (SNPs) genotyped in 270 individuals from four geographically diverse populations and includes 25-35% of common SNP variation in the populations surveyed. The map is estimated to capture untyped common variation with an average maximum r 2 of between 0.9 and 0.96 depending on population. We demonstrate that the current generation of commercial genome-wide genotyping products captures common Phase II SNPs with an average maximum r 2 of up to 0.8 in African and up to 0.95 in non-African populations, and that potential gains in power in association studies can be obtained through imputation. These data also reveal novel aspects of the structure of linkage disequilibrium. We show that 10-30% of pairs of individuals within a population share at least one region of extended genetic identity arising from recent ancestry and that up to 1% of all common variants are untaggable, primarily because they lie within recombination hotspots. We show that recombination rates vary systematically around genes and between genes of different function. Finally, we demonstrate increased differentiation at non-synonymous, compared to synonymous, SNPs, resulting from systematic differences in the strength or efficacy of natural selection between populations. ©2007 Nature Publishing Group., link_to_OA_fulltext

Although much progress has been made in the understanding of the ontogeny and function of dendritic cells (DCs), the transcriptional regulation of the lineage commitment and functional specialization of DCs in vivo remains poorly understood. We made a comprehensive comparative analysis of CD8 +, CD103 +, CD11b + and plasmacytoid DC subsets, as well as macrophage DC precursors and common DC precursors, across the entire immune system. Here we characterized candidate transcriptional activators involved in the commitment of myeloid progenitor cells to the DC lineage and predicted regulators of DC functional diversity in tissues. We identified a molecular signature that distinguished tissue DCs from macrophages. We also identified a transcriptional program expressed specifically during the steady-state migration of tissue DCs to the draining lymph nodes that may control tolerance to self tissue antigens. © 2012 Nature America, Inc. All rights reserved.

With the advent of dense maps of human genetic variation, it is now possible to detect positive natural selection across the human genome. Here we report an analysis of over 3 million polymorphisms from the International HapMap Project Phase 2 (HapMap2). We used 'long-range haplotype' methods, which were developed to identify alleles segregating in a population that have undergone recent selection, and we also developed new methods that are based on cross-population comparisons to discover alleles that have swept to near-fixation within a population. The analysis reveals more than 300 strong candidate regions. Focusing on the strongest 22 regions, we develop a heuristic for scrutinizing these regions to identify candidate targets of selection. In a complementary analysis, we identify 26 non-synonymous, coding, single nucleotide polymorphisms showing regional evidence of positive selection. Examination of these candidates highlights three cases in which two genes in a common biological process have apparently undergone positive selection in the same population:LARGE and DMD, both related to infection by the Lassa virus, in West Africa;SLC24A5 and SLC45A2, both involved in skin pigmentation, in Europe; and EDAR and EDA2R, both involved in development of hair follicles, in Asia. ©2007 Nature Publishing Group., link_to_OA_fulltext

The creep deformation of two near-γ titanium aluminide alloys with equiaxed and lamellar structures have been studied to understand their behaviour as a function of microstructural evolution during the early stages of creep. The lamellar alloys exhibit more pronounced hardening during the primary stage of creep leading to a much better creep resistance and a minimum creep rate two orders of magnitude lower than that of the equiaxed alloys. TEM observations have confirmed that the active deformation mechanisms are the same for both alloys and microstructural states, namely extensive slip of single 1/2(110) dislocations and mechanical twinning. The latter has been comfirmed to occur in a fraction of the grains that never exceeds 50% while 1/2(110) dislocations are active within all the y grains. The twins are only responsible for a small amount of strain but they lead to a subdivision of the microstructure and determine (directly or indirectly) the hardening process observed during the primary stage of creep. During the secondary stage the creep rate is determined by the unblocking of pinned dislocations by processes such as a pipe diffusion or cross-slip that allow thermally activated glide of 1/2(110) dislocations within the y matrix.

Trabajo presentado en el MRS Fall Meeting, celebrado en Boston, MA, (Estados Unidos), del 2 al 5 de diciembre de 1996, Different Ti-Al alloys with grain sizes ranging from 7μm to 320 nm have been prepared by consolidation of atomised and mechanically milled powders of nominal composition Ti-48Al-2Mn-2Nb and containing carbon additions. The materials obtained consist of equiaxed γ grains containing a distribution of α2 phase mostly along grain or powder boundaries. The high flow strength and low fracture toughness obtained from these materials have been correlated to the fine scale of the microstructure and the transfer of slip across adjacent γ grains. The existence of stress concentrations at boundaries between γ grains leads to emission of curved dislocations and twins. The low mobility of emitted dislocations is responsible for the lack of tensile ductility in these alloys which fail by microcrack formation at grain boundaries.